1. Field of the Invention
The present invention relates generally to a capacitor discharge welding process and, more particularly, to such a process adapted to join metallic braided cable to solid metallic, intermetallic or metallic composite substrates.
2. Description of the Prior Art
With the present state of the art, if it is desired to join a braided cable to an electrode, a known brazing, soldering or resistance welding process must be utilized. However, each of these processes has their shortcomings. Both the soldering and brazing processes require the use of harmful welding agents such as lead-based materials or toxic fluoride-containing fluxes. The resistance welding process has the drawback of being a high heat input process. The generation of high heat can dramatically change the microstructure of the braided cable or the electrode and sometimes weakens the base metal of the electrode adjacent the heat affected zone created during the welding process. Changes in metal microstructure or the weakening of the electrode adjacent its heat affected zone can obviously result in failures during electrode use.
As an alternative to the known brazing, soldering or resistance welding processes presently used to join braided cables to electrodes, it would be desirable to utilize a welding process which does not generate high heat during operation and which does not require the use of harmful welding agents. The capacitor discharge welding process could be such an alternative. The capacitor discharge welding process itself generally involves gravity assisted, axial impact of cylindrical specimens with subsequent arcing and melting (and thus joining) by the discharge of a capacitor bank. During impact the arc is extinguished, and any excess molten metal is expelled as solidification occurs. Attractive features of the capacitor discharge process include the suppression of fusion zone porosity due to hydrogen uptake and a minimal heat affected zone. In addition the welds tend not to crack because of the compressive forces developed during the welding cycle. Thus the microstructure near the weld is characteristic of the base metal and is affected little by the joining process. Finally, the width of the fusion zone can be controlled by varying the welding parameters, which in turn control the cooling rate.
It is apparent from the foregoing that the capacitor discharge welding process for joining braided cables to solid electrodes would be a desirable alternative to known brazing, soldering and resistance welding processes. However, the capacitor discharge welding process has not heretofore been used successfully to join a braided cable such as a copper electrical cable and a solid copper electrode such as a terminal due to the flexible nature of braided cables. Since braided cables are flexible, the individual cable strands forming the cable unwrap slightly upon cable cutting in preparation for welding. This slight unwrapping adversely affects the capacitor discharge welding process and results in the achievement of a less than satisfactory weld.
Consequently, there is a need for an improved capacitor discharge welding process which takes into account the flexible nature of braided cables and results in the formation of a metallurgically strong weld joint between the braided cable and the solid electrode after the capacitor discharge welding process is complete.